The RAD52 gene in Saccharomyces cerevisiae controls the repair of ionizing radiation-induced DNA double-strand breaks, radiation-induced spontaneous mitotic recombination, and recombination during meiosis. Utilizing an antibody raised against a Neurospora crassa deoxyribonuclease, we had shown that an antigentically related enzyme could be identified from yeast and that this enzyme is controlled by the RAD52 gene. Uisng a Lambdagtll vector expression library that contains genomic yeast DNA and the antibody as a probe, we have identified a segment of DNA that codes for cross-reacting material. A sequence from a yeast genomic library has been identified that hybridizes with this segment. Introduction of this into a Rad+ strain leads to enhanced synthesis of cross-reacting material. Since this sequence contains the putative gene for the RAD52 controlled nuclease, the role of the gene in recombination, repair and normal growth will be determined by inactivating the corresponding gene in the genome and determining the consequences. In the process, it will also be possible to map the gene.